Reenforcing bar for concrete



Patented Nov. 13, 1934 UNITED STATES "1' 1;.T|-:`1\1T oFFicg 1,980,661; REENFORCING BAR FOR CONCRETE Charles Stratton Davis, Pittsburgh, Pa.` Application January 20, 1932, Serial No.`587,699

1 claim. (ci, 'z2-111)` The 'following is a full, clear and exact description, reference being vhad to the accompanying drawing, forming part of this specification,

in which:

Figure 1 is an isometric projection showing invention Figure 2 isa similar View of a modified form; Figure 3 is an enlarged cross sectional diagram of the form of vFigure 1. Figure 4 is a similar diagram of the form of Figure 2;

Figure 5 is an isometric projection of a portion of the breakdown bar f or rolling the form of Figure 1 in one pass ofA rolling mill; and

Figure 6 is a partial front elevation of a portion of the rolls for showing the pass for rolling the form of Figure 1.

My invention relates to bars for reenforcing concrete, and is designed to provide a bar of the same cross sectional shape throughout to avoid distortions of stress lines; to have a ratio of perimeter to cross sectional area greater than that of a square or round bar of the same cross earlier stages of this art, plain round and plain square bars were used, and later, in order to reduce the length of bars required to develop full tensile strength, square bars were twisted and bars of different shapes otherwise deformed.

Plain square or round bars are free from the objection to distortion of stress lines, but the ratio of perimeter to cross sectional area is relatively low, and hence longer bars are required to develop full tensile strength from their bond strength with concrete.

Twisted bars are more expensive to manufacture than plain bars and, unless annealed, lack homogeneity, since the outer fibres are stressed beyond their yield points in giving a permanent twist, while the central fibres are not altered. The stressing of the outer bres beyond their yield points changes their stressstrain curves under test, and hence the metal in such twisted bars lacks the desired uniformity of character.

The stress lines in the outer bres of a twisted bar follow the spiral lines of twist, while those of the central bres are straight along the axis, which results in lack of uniformity of stress lines. v

Deformed bars are more expensive to manufacture than plain bars on account of the extra expense of preparing the rolls which Wear rapidly; rBars having raised deformationscontain material not effective for tensile stresses and l hence are not economical. The stress'lines in 65 a deformed bar are distorted by its deformations and consequently lack uniformity. The development of bond strength through these deformations is not uniformly distributed, and hence'the concrete is liable to over-stressing at points 'of 70 deformation.

My invention is designed to provide a bar having the same cross sectional shape throughout its length to avoid distortion of stress lines, but having a ratio of perimeter to cross sectional area greater than that of a square bar, and of course, greater than that of a round bar; so

' that the length of bar required for bond strength to fully develop its tensile strength may be as short as possible, while at the same time it may be rolled in a rolling mill under ordinary practice.

To that end, the bar has throughout its length a cross sectional shape of a -pointed star with the points located at the apices of a circumscribing hexagon-either regular or irregularthe reentrant angles Z Figure 3 between these points being sufficiently small to give a ratio of periphery to cross sectional area greater than that of a square bar and yet provide the proper draft or taper for rolling.

In the preferred form shown in Figures 1 and 3', the bar 2 has six points which are coincident with the apices of the regular circumscribing hexagon at the points al, a2, a3, a4, a5, a6. In the diagram of Figure 3, o is the center of the star. The'lines oil-a4, z2-a5, and cl3-a6 through the center are long diameters, each twice the radial length of the star. The lines lil-b4, Z22-b5, and b3-b6, each through the center of the star, are short diameters, each twice the short radial length of the star. The angles a: between the peripheral lines of the star and the sides of the hexagon are all the same, and these angles are suflicient to provide a ratio of per- I'15 imeter to cross sectional area greater than the corresponding ratio of a square bar, so that the ratio of surface area to volume is greater than that in a square bar. These angles, however, are y ,q limited to give proper draft or taper for rolling ",110

purposes, so that any two lines of the 'periphery of the star, between which there are two intervening lines forming a reentrant angle will be sufficiently divergent to conform to good rolling mill practice, so that any long diameter such as z2- a5 may lie along the line of contact, d-d, Figure 6, between the rolls.

I prefer that the angles :l: be less than (28 as shown in Figure 3)-, sorthat where the line :z2-'a5 coincides with the line of contact between the rolls, the lines L1-b1 and as-b5 and also all-b2 and aflb4 shall be sufficiently divergent to give the draft or taper requiredfor good rolling mill practice; but these angles shall not be less than 12 in order that the ratio of periphery to cross sectional areashall always exceed the ratio of perimeter to cross sectional area of a square bar.

The perimeterof a round bar Y sectional area of one inch is 3.555 inches; that Yof, ajsquare bar of the same area is 4.000 inches; and that of myV preferred `form with the 28 angle `A`shown in Figure 3 is 5.064 inches, so that its ratio of perimeter to cross sectional area is 225% greater thanvthatof around bar and -.J.6-.i ;%v greater than that of a square bar. In the form of `I'igures 2 and 4, the irregular Astar section vfor Zahasts points a1, a2, a3, a", a5 and (1,6 at the corners of an irregular circumscrihing hexagon with its long diameter z2-a5 `falling, along the line of contact between the rolls- I-h,e1angles y of Figure 4 between the lines vvgif, the,perfipheryfof4 the star and the sides of the irregular vcircumscribing hexagon shall not `loe larger than is necessary to make the lines :z3- b2 Aand L4-b4, and also a---b1 and a6-b5 sumciently divergent to provide draft or taperI for rolling under good rolling mill practice; but they shall be large enough to make the ratio of perimeter to area of the star greater than that of a rectangle of the same area and having be rolled therefrom in one pass as shown in AFigure 6. The `breakdown bar for the form of Figures 2' andi! will, of course, be correspondingly Ymoxiifwd- The advantages of my invention lie in its high y bond strength per unit of length, due to its havinga cross great ratio of perimeter to cross sectional area, resulting in a shorter length of barthan with either plain square or round bars);v *iin4 its r`freedom from distorted stress lines; `in they uniformity of; its bondsstreng-th per -unit of length; and in that it may be produced at a low cost, -dueto its being of the same cross ysectional Shape throughout and easily rol-led.

Variations may be made in the anglesnsize, etc., withoutl departing lfrom my invention.

I claim: Y, Y

A reenforcing bar for cencretebeng in the form of a prism -between anyVv two parallel cross sectional planes whose uniform cross section is that of a (l-pointed star` Y v CHARLES s'rRA''roN `mivrs.

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